Economic production from an unconventional gas reservoir is possible only if a complex fracture network can be created that connects a huge reservoir area to the wellbore effectively. This fracture network can be created by hydraulic fracturing. Several techniques can be used to present hydraulic fractures in a simulation model. In a simple model it is assumed that the fractures lie in the single plane of local tartan grid cells that best approximates the true geometric orientation of the fracture. The local refinement is symmetrically placed within the plane of host cells and has small cells close to the fracture that logarithmically increase in size away from the fracture. Explicitly calculated transmissibility multipliers on the faces of the cells that intersect the fracture are used to model the flow between matrix and the hydraulic fracture. The spacing and conductivity of the hydraulic fractures are critical parameters that control well performance.
A new reservoir modeling and simulation technique has been developed for these complex fracture networks that combines discrete fracture network (DFN) modeling and unstructured fracture (UF) modelingto simulate well performance and improve stimulation design. This is very important for modeling and simulation of a well with hydraulic fractures in a shale gas reservoir with natural fractures.
Results from this new model show a gas shale reservoir can be drained more effectively if a complex fracture network can be created by hydraulic fracture stimulation. In addition to a large increase in the production, the number of fracture treatment stages can be reduced if a high-conductivity fracture can be created, adding to the economic viability of the development of unconventional gas sources. The modeling and simulation technique presented in this paper can help identify stimulation and completion strategies that will significantly improve well performance and ultimate recovery from an unconventional gas reservoir.